Vehicles as a rule have a vehicle brake arrangement, in which by means of a hydraulic fluid a braking operation at wheel brakes of a vehicle is achieved. However, increasingly vehicles also have an electric machine, such as an electric motor, which is used to drive the vehicle at least as back-up to an internal combustion engine. Compared to an internal combustion engine, the electric machine offers the advantage that in a so-called regenerative braking operation it may be operated as a generator in order to charge a vehicle battery. The chemical energy stored in the charged battery is then reused in a motor mode of the electric machine to drive the motor vehicle.
Thus, whereas in the normal braking mode kinetic energy of the vehicle is converted to thermal energy as a result of the friction-locking interaction of brake shoes and brake disks at the wheel brakes, what occurs in the regenerative braking mode is a charging of the vehicle battery. Since in the regenerative braking mode the slowing-down of the motor vehicle is effected by means of the electric machine, the wheel brakes may remain unactuated. As a rule this is even desired since any kinetic energy converted to thermal energy at the wheel brakes is no longer available for charging the vehicle battery.
Control of the splitting of the components that implement the braking—vehicle brake system and electric machine—is effected by means of various control devices and additional devices, such as for example additional valves.
Thus, DE 10 2009 039 207 A1 describes a regenerative vehicle brake and an operating method for a regenerative vehicle brake, which comprises a regeneration device that enables an asymmetric regenerative braking mode for a first and a second hydraulic brake circuit. A vehicle having such a regenerative vehicle brake comprises a generator, wherein in the regenerative braking mode a brake pressure build-up at wheel brakes of the first brake circuit is effected at least in a reduced manner and a brake pressure build-up at wheel brakes of the second brake circuit is effected in a substantially unreduced manner. For this purpose the regeneration device comprises at least delay devices.
The regenerative vehicle brake described in DE 10 2009 039 207 A1, on the other hand, again comprises additional components for controlling the regenerative vehicle brake and for achieving a combined braking of a purely hydraulic vehicle brake arrangement and an electric machine.
DE 11 2008 000 673 T5 relates to a vehicle brake system having an electric motor that generates a wheel-driving force or a regenerative wheel-braking force. In order to improve the actuating sensation of a brake pedal in a vehicle having an electric motor that carries out the regenerative braking, has a first wheel-braking-force generating device, by means of which first wheel braking forces that are generated by the regenerative braking are applied to wheels, and a second wheel-braking-force generating device, which adjusts the pressure of a working fluid that is generated by the actuating pressure that is applied by a driver to a brake pedal. Second wheel-braking forces are applied to wheels in that the pressure is transmitted to the respective wheels, wherein the vehicle braking device applies the requisite wheel-braking forces, which correspond to the actuation of the brake pedal by the driver, to the wheels. A third wheel-braking-force generating device applies third wheel-braking forces, which differ from the first and second wheel-braking forces, to the wheels. A brake control device compensates the braking forces, which correspond to the reduction of the first wheel-braking forces, by means of third wheel-braking forces of the third wheel-braking-force generating device when the first wheel-braking forces decrease as a result of the deterioration of the conversion efficiency of the electrical energy, this occurring during the regenerative braking, while the first wheel-braking forces are applied to the wheels.
DE 10 2005 024 339 A1 relates to a vehicle braking device having a hydraulic braking device for boosting a brake-actuating force by means of a booster device upon a brake actuation for applying a basic fluid pressure, which is generated as a function of the boosted brake-actuating force, to wheel cylinders of wheels, so that a basic hydraulic braking force is generated at the wheels. A pump is used to generate and apply a controlled fluid pressure to the wheel cylinders, so that a controlled hydraulic braking force is generated at the wheels. A brake-actuating-state detection device is used to detect the brake actuating state. A regenerative braking device has the effect that an electric motor generates a regenerative braking force in accordance with the brake actuating state at the wheels, which are driven by the electric motor. A variation detection device detects the variation of an actual regenerative braking force that is actually generated by the regenerative braking device. A braking-force compensation device generates the controlled fluid pressure by driving the pump of the hydraulic braking device, so that a controlled hydraulic braking force is generated at the wheels in order to compensate the deficiency of the regenerative braking force because of the variation, which deficiency is detected by the variation detection device.
DE 10 2006 055 799 A1 relates to a method of regeneratively braking a vehicle, by means of a hydraulic or pneumatic brake system, an electromechanical brake system and a generator, wherein each of the systems contributes a specific share of a desired total deceleration of the vehicle. A braking operation may be carried out particularly easily and with a high degree of efficiency if the share of the electromechanical braking device is regulated in dependence upon the share of the generator.
DE 10 2010 040 190 A1 relates to a brake system and a method of operating a brake system having two brake circuits, having a recuperative brake, in particular an electric generator, a master cylinder and a brake pedal for improving the environmental compatibility and the energy efficiency, the full availability of the torque at low rotational speeds as well as the lower noise generation. In order with such a brake system to utilize the maximum available generator braking torque and hence also the maximum possible energy yield, the actuation of the brake pedal has to be uncoupled from the direct feed-through to the wheel brakes. Upon a braking request of the driver with an associated setpoint braking torque, given a first condition at least one outlet valve is opened and brake fluid of an associated brake fluid volume is conveyed into at least one accumulator. Then, given a second condition the at least one outlet valve is closed, wherein the first condition exists if a braking quantity corresponding to the braking request does not exceed a defined minimum value, and wherein the second condition exists if the braking fluid volume has flowed into the accumulator.
The prior art however does not include any vehicle brake systems, which offer a regenerative braking mode for a vehicle having a hydraulic vehicle brake arrangement and an electric machine, in which a splitting of the vehicle components providing the braking is controlled without additional devices and with which moreover an optimized braking and the known properties of a purely hydraulic brake arrangement are made available to a driver.
Additional devices not only have a negative impact on the additionally required space, they also give rise to higher costs and a greater control outlay. Furthermore, in vehicles having such vehicle brakes yet more devices are often provided, which simulate for the driver the impression and the response of a purely hydraulic brake arrangement. These devices likewise lead to a greater control outlay.